TOEFL READING PRACTICE WITH ANSWERS
TOEFL 5 (READING PASSAGE 5)
|
Questions
32-44
Bloodhounds
are biologically adapted to trailing their prey. The process by which the
nose recognizes an odor is not fully understood, but there are apparently
specific receptor sites for specific odors. In one explanation, recognition
occurs when a scent molecule fits into its corresponding receptor site,
like a key into a lock, causing a mechanical or chemical change in the cell.
Bloodhounds apparently have denser concentrations of receptor sites tuned
to human scents.
When
a bloodhound trails a human being, what does it actually smell? The human
body, which consists of about 60 trillion living cells, sheds exposed skin
at a rate of 50 million cells a day. So even a trail that has been
dispersed by breezes may still seem rich to a bloodhound. The body also produces
about 31 to 50 ounces of sweat a day. Neither this fluid nor the shed skin
cells have much odor by themselves, but the bacteria working on both
substances is another matter. One microbiologist estimates the resident
bacteria population of a clean square centimeter of skin on the human
shoulder at "multiples of a million." As they go about their
daily business breaking down lipids, or fatty substances, on the skin,
these bacteria release volatile substances that usually strike the
bloodhound's nose as an entire constellation of distinctive scents.
|
45. What does the passage mainly discuss?
(A) Why people choose bloodhounds for household pets
(B) How a bloodhound's sense of smell works
(C) How humans compensate for an underdeveloped sense of smell
(D) The way in which bacteria work on skin cells and body sweat.
|
46. The author compares a scent molecule with a
(A) key
(B) lock
(C) cell
(D) bloodhound
|
47. In line 7, the word "it" refers to
(A) bloodhound
(B) human being
(C) smell
(D) body
|
48. According to the passage, how many cells of skin does the human
body rid itself of every day?
(A) 60 trillion
(B) 50 million
(C) 1 million
(D) Between 31 and 50
|
49. In line 10, the word "rich" is used to mean that a
trail is
(A) paved with precious materials
(B) a profitable business to get into
(C) a very costly undertaking
(D) filled with an abundance of clues.
|
50. Which of the following acts as a stimulus in the production of
the human scent?
(A) Sweat
(B) Dead skin cells
(C) Bacteria
(D) Fatty substances
|
|
CLICK HERE FOR READING PASSAGE 4
CLICK HERE FOR READING POST TEST
ANSWER KEY
45. B
46. A
47. A
48. B
49. D
50. C
|
No comments:
Post a Comment
thank you for visiting my blog and for your nice comments